This invention relates to insert molded articles in which a substrate or film is back molded with an injection molded material.
In a typical in-mold decorating process, a printed substrate is formed into a three-dimensional shape and placed into a mold. Molten resin is then injected into the mold cavity space behind the formed substrate, forming a single molded part.
IMD may involve two types of film processes. According to one process, the film is a permanent fixture of the finished good. In this case, the film can act as the aesthetic effect carrier, and/or as a protective layer for the substrate resin, the ink, or both. Good adhesion is required between the film, such as a polycarbonate type film, and the substrate resin.
According to another process, the film may be a temporary carrier for the aesthetic effect. In this case the substrate resin is back-molded on the IMD film and the film is subsequently peeled off of the substrate resin, leaving the aesthetic material/design behind on the substrate resin. Good adhesion is not desired between the film, which may be a poly(ethylene terephthalate) type film and the substrate resin.
For both in-mold decorating (IMD) applications, ink washout of the IMD film is an inherent problem. In IMD applications, an ink (or other aesthetic enhancement) bearing or containing film is back-molded by a substrate resin for structural support. During the back-molding of the substrate material, the aesthetic ink or effect material is often sandwiched between the IMD film and the substrate resin. The resulting shear from the back-molding injection of the substrate resin material against the IMD film, coupled with the heat of the molten substrate resin can often cause the ink (or aesthetic bearing material) to detach itself from the IMD film. This results in an area of decreased ink concentration, or xe2x80x9cwashout.xe2x80x9d This washout is caused by several processing factors of the substrate resin, including processing temperature and injection shear.
Other challenges during the IMD process are foil breakage/wrinkling, again as a result of the high pressures and temperatures needed to back mold.
A resin used as an IMD substrate is a blend of polycarbonate (PC) with ABS (acrylonitrile-butadiene-styrene), such as Cycoloy produced by GE Plastics. One of the reasons is the superior shear thinning behavior of PC/ABS blends, which enables the molder to fill the mold at lower injection rates and temperatures.
U.S. Pat. No. 3,654,062 to Loew describes a molded decorative plaque having a laminated facing sheet which has the configuration of the mold. Heated plastic is injection molded behind the sheet to form the plaque. U.S. Pat. No. 6,117,384 to Laurin et al. describes a process where colors are decorated into a single film which is then incorporated with a molten resin injected behind the film to produce a permanently bonded three-dimensional piece. U.S. Pat. No. 4,391,954 to Scott describes a thermoplastic molding composition comprising an aromatic carbonate polymer and a polyester derived from a cyclohexanedimethanol. U.S. Pat. No. 4,125,572 to Scott describes a thermoplastic molding composition comprising an aromatic carbonate polymer and a polyester derived from an aliphatic or cycloaliphatic diol. U.S. Pat. No. 4,662,966 to Nissha Printing Co. Ltd. describes a transfer printing machine where designs of a diffusible dye on a transfer sheet is transferred to heated articles.
It is desired to have a material which has improved chemical resistance and can obtain low temperature impact with special effects and high clarity. The chemical resistance of many transparent, amorphous materials is not sufficient towards chemicals like oleic acid and/or coppertone, which are considered to be important chemicals in qualifying new materials in the telecom/electronics business. In some cases it is preferred to have a translucent material, since some light scattering can contribute to the desired effect.
A molded structure that comprises a decorative film or substrate, and an adjacent injection molded polymeric base comprising a substantially transparent cycloaliphatic polyester resin. In one embodiment, the substrate has at least one opening which exposes the transparent polymeric base resin to the exterior of the molded article.
According to a molding method, a printed substrate is formed into a three-dimensional shape and placed into a mold. Molten resin is then injected into the mold cavity space behind the formed substrate, forming a single molded part.
The use of a transparent cycloaliphatic polyester resin as the injection molded base material obviates disadvantages encountered with non-transparent PC/ABS type blends. Lack of transparency may be a significant drawback in certain applications. For instance, for some cell phones, a film (PET) with ink patterns is back molded with a transparent resin to mold the complete front cover. This is done so that information can be visually accessed by the product""s user through a transparent window which is integrated into the structural resin of the product""s design. During the back molding, ink may be transferred from the film to the transparent resin and then removed, resulting in a decorated front cover. An example of transfer printing the Nissha process. See U.S. Pat. No. 4,662,966 to Sumi et al.
For some applications, the film of substrate material may be a permanent aesthetic part of the finished product. For some wireless personal electronic applications which may use a film such as a polycarbonate (PC) film with ink patterns which is back molded with a transparent resin to mold the complete product housing. The transparent base material is molded to create a transparent window. Data may be transferred to/from the electronic product to its server by IR through the transparent window which is integrated into the structural resin of the product. Holes in the film expose the transparent injected molded base resin for either data transfer or aesthetic purposes.
One possibility for a transparent material is polycarbonate (PC). Typically, the processing temperature and injection shear (viscosity) of PC results in washout of ink on the IMD film at the injection gate. Other higher flow transparent materials (like LEXAN SP, a super high flow PC grade produced by GE Plastics) give an improvement in terms of viscosity, but have a very small processing window and as such are not very robust. Even these higher flow materials are not suitable for thinner-walled IMD parts where their fast injection speeds will still result in IMD washout and other issues as described above (e.g. foil breakage). In addition, physical properties (especially impact) of LEXAN SP and other such high-flow products are also not sufficient for use in many IMD applications.
Cycloaliphatic polyester/Polycarbonate blends and/or cycloaliphatic polyester/Polycarbonate/impact modified blends are utilized as a back-molded resin for in-mold decorated (IMD) film applications. Transparent blends of Polycarbonate (PC) and poly(cyclohexane dimethanol cyclohexane dicarboxylate) (PCCD) possess lower processing temperatures and improved flow characteristics over standard PC materials. This results in slower injection speeds and lower injection shear in an injection molded IMD part when compared to other transparent back-molding substrate resins (such as LEXAN SP) for in-mold decorating (IMD) applications. This in turn results in a decrease of the washout effect in IMD applications. These blends also offer superior chemical resistance and ductility to that of most transparent resin materials. The complete miscibility of this system allows the properties of the resulting blend to be dialed in, via blend ratio, while still maintaining transparency.
Two types of cycloaliphatic polyesters may desirable can be used with BPA-based polycarbonate to give the compositions and articles of this invention. The most preferred polyester molecules are derived from cycloaliphatic diol and cycloaliphatic diacid compounds, specifically polycyclohexane dimethanol cyclohexyl dicarboxylate (PCCD). The polyester having only one cyclic unit may also be useful.
In addition, PCCD and PC can be blended with certain impact modifiers (IM) at such ratios as to match the refractive index (RI) of the impact modifier to that of the PC/PCCD blend and therefore still retain transparency. In addition to the characteristics of PC/PCCD resins, these PC/PCCD/IM blends possess improved low temperature ductility which can be a key requirements for IMD applications, for example, cellphone covers.
The present invention is directed to multi-layer plastic articles and methods for making such articles. More particularly, the articles comprise a base layer of an injection molded thermoplastic and surface layer of a decorated film. The multi-layer film comprises a fluoride polymer layer laminated to a polycarbonate layer.
A method for producing multi-layered films with the properties of: formable, low birefringence, chemical, and UV radiation resistance, and optical transparency is set forth. These laminated films are well suited for exterior automotive insert mold decoration (IMD) applications. IMD is the process by which the formed, and decorated film is placed in the mold and the thermoplastic melt, which forms the base layer, is injection molded to the exposed surface of the film
According to one embodiment, molded articles are prepared by the steps of:
(1) providing a decorative substrate, such as polycarbonate, having one or more colors on a surface, for example by screen printing;
(2) forming and trimming the printed substrate into a three-dimensional shape;
(5) fitting the printed substrate into a mold having a surface which matches the three-dimensional shape of the substrate; and
(6) injecting a substantially transparent resin comprising a blend of cycloaliphatic polyester resin and a polycarbonate resin, into the mold cavity behind the printed substrate to produce a one-piece, permanently bonded three-dimensional product.
The injection molded substantially transparent resin comprises a transparent cycloaliphatic polyester resin and more preferably a cycloaliphatic polyester resin blended with polycarbonate.
In cases where the polycarbonate has a high Tg and is difficult to process the cycloaliphatic polyester acts to lower the PC Tg. A blend with a cycloaliphatic polyester reduces Tg making melt processing easier while the blend has excellent optical properties overall. The most preferred materials will be blends where the polyester has both cycloaliphatic diacid and cycloaliphatic diol components specifically polycyclohexane dimethanol cyclohexyl dicarboxylate (PCCD). The preferred polycarbonate will be composed of units of BPA, SBI bis phenol, aryl substituted bisphenols, cycloaliphatic bisphenols and mixtures thereof. It is contemplated that acidic phosphorus based stabilizers are useful to retard melt reaction of the cycloaliphatic polyester and polycarbonate resin and improve color.
The ratio of cycloaliphatic polyester to polycarbonate in the range of 40:60 to 5:95% by weight of the entire mixture is preferred. Blends from 50:50 to 30:70 are most preferred.
The cycloaliphatic polyester resin comprises a polyester having repeating units of the formula I: 
where at least one R or R1 is a cycloalkyl containing radical.
The polyester is a condensation product where R is the residue of an aryl, alkane or cycloalkane containing diol having 6 to 20 carbon atoms or chemical equivalent thereof, and R1 is the decarboxylated residue derived from an aryl, aliphatic or cycloalkane containing diacid of 6 to 20 carbon atoms or chemical equivalent thereof with the proviso that at least one R or R1 is cycloaliphatic. Preferred polyesters of the invention will have both R and R1 cycloaliphatic.
The present cycloaliphatic polyesters are condensation products of aliphatic diacids, or chemical equivalents and aliphatic diols, or chemical equivalents. The present cycloaliphatic polyesters may be formed from mixtures of aliphatic diacids and aliphatic diols but must contain at least 50 mole % of cyclic diacid and/or cyclic diol components, the remainder, if any, being linear aliphatic diacids and/or diols. The cyclic components are necessary to impart good rigidity to the polyester and to allow the formation of transparent blends due to favorable interaction with the polycarbonate resin.
The polyester resins are typically obtained through the condensation or ester interchange polymerization of the diol or diol equivalent component with the diacid or diacid chemical equivalent component.
R and R1 are preferably cycloalkyl radicals independently selected from the following formula: 
The preferred cycloaliphatic radical R1 is derived from the 1,4-cyclohexyl diacids and most preferably greater than 70 mole % thereof in the form of the trans isomer. The preferred cycloaliphatic radical R is derived from the 1,4-cyclohexyl primary diols such as 1,4-cyclohexyl dimethanol, most preferably more than 70 mole % thereof in the form of the trans isomer.
Other diols useful in the preparation of the polyester resins of the present invention are straight chain, branched, or cycloaliphatic alkane diols and may contain from 2 to 16 carbon atoms. Examples of such diols include but are not limited to ethylene glycol; propylene glycol, i.e., 1,2- and 1,3-propylene glycol; 2,2-dimethyl-1,3-propane diol; 2-ethyl, 2-methyl, 1,3-propane diol; 1,3- and 1,5-pentane diol; dipropylene glycol; 2-methyl-1 ,5-pentane diol; 1,6-hexane diol; dimethanol decalin, dimethanol bicyclo octane; 1,4-cyclohexane dimethanol and particularly its cis- and trans-isomers; 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCBD), triethylene glycol; 1,10-decane diol; and mixtures of any of the foregoing. Preferably a cycloaliphatic diol or chemical equivalent thereof and particularly 1,4-cyclohexane dimethanol or its chemical equivalents are used as the diol component.
Chemical equivalents to the diols include esters, such as dialkylesters, diaryl esters and the like.
The diacids useful in the preparation of the aliphatic polyester resins of the present invention preferably are cycloaliphatic diacids. This is meant to include carboxylic acids having two carboxyl groups each of which is attached to a saturated carbon. Preferred diacids are cyclo or bicyclo aliphatic acids, for example, decahydro naphthalene dicarboxylic acids, norbornene dicarboxylic acids, bicyclo octane dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid or chemical equivalents, and most preferred is trans-1,4-cyclohexanedicarboxylic acid or chemical equivalent. Linear dicarboxylic acids like adipic acid, azelaic acid, dicarboxyl dodecanoic acid and succinic acid may also be useful.
Cyclohexane dicarboxylic acids and their chemical equivalents can be prepared, for example, by the hydrogenation of cycloaromatic diacids and corresponding derivatives such as isophthalic acid, terephthalic acid or naphthalenic acid in a suitable solvent such as water or acetic acid using a suitable catalysts such as rhodium supported on a carrier such as carbon or alumina. See, Friefelder et al., Journal of Organic Chemistry, 31, 3438 (1966); U.S. Pat. Nos. 2,675,390 and 4,754,064. They may also be prepared by the use of an inert liquid medium in which a phthalic acid is at least partially soluble under reaction conditions and with a catalyst of palladium or ruthenium on carbon or silica. See U.S. Pat. Nos. 2,888,484 and 3,444,237.
Typically, in the hydrogenation, two isomers are obtained in which the carboxylic acid groups are in cis- or trans-positions. The cis- and trans-isomers can be separated by crystallization with or without a solvent, for example, n-heptane, or by distillation. The cis-isomer tends to blend better; however, the trans-isomer has higher melting and crystallization temperatures and may be preferred. Mixtures of the cis- and trans-isomers are useful herein as well.
When the mixture of isomers or more than one diacid or diol is used, a copolyester or a mixture of two polyesters may be used as the present cycloaliphatic polyester resin.
Chemical equivalents of these diacids include esters, alkyl esters, e.g., dialkyl esters, diaryl esters, anhydrides, salts, acid chlorides, acid bromides, and the like. The preferred chemical equivalents comprise the dialkyl esters of the cycloaliphatic diacids, and the most favored chemical equivalent comprises the dimethyl ester of the acid, particularly dimethyl-1,4-cyclohexane-dicarboxylate.
A preferred cycloaliphatic polyester is poly(cyclohexane-1,4-dimethylene cyclohexane-1,4-dicarboxylate) also referred to as poly(1,4-cyclohexane-dimethanol-1,4-dicarboxylate) (PCCD) which has recurring units of formula II: 
With reference to the previously set forth general formula, for PCCD, R is derived from 1,4 cyclohexane dimethanol; and R1 is a cyclohexane ring derived from cyclohexanedicarboxylate or a chemical equivalent thereof. The favored PCCD has a cis/trans formula.
The polyester polymerization reaction is generally run in the melt in the presence of a suitable catalyst such as a tetrakis(2-ethyl hexyl)titanate, in a suitable amount, typically about 50 to 200 ppm of titanium based upon the final product.
The preferred aliphatic polyesters used in the present transparent molding compositions have a glass transition temperature (Tg) which is above 50xc2x0 C., more preferably above 80xc2x0 C. and most preferably above about 100oC.
Also contemplated herein are the above polyesters with from about 1 to about 50 percent by weight, of units derived from polymeric aliphatic acids and/or polymeric aliphatic polyols to form copolyesters. The aliphatic polyols include glycols, such as poly(ethylene glycol) or poly(butylene glycol). Such polyesters can be made following the teachings of, for example, U.S. Pat. Nos. 2,465,319 and 3,047,539.
Polycarbonates useful in the invention comprise the divalent residue of dihydric phenols, Ar xe2x80x2, bonded through a carbonate linkage and are preferably represented by the general formula III: 
wherein A is a divalent hydrocarbon radical containing from 1 to about 15 carbon atoms or a substituted divalent hydrocarbon radical containing from 1 to about 15 carbon atoms; each X is independently selected from the group consisting of hydrogen, halogen, and a monovalent hydrocarbon radical such as an alkyl group of from 1 to about 8 carbon atoms, an aryl group of from 6 to about 18 carbon atoms, an arylalkyl group of from 7 to about 14 carbon atoms, an alkoxy group of from 1 to about 8 carbon atoms; and m is 0 or 1 and n is an integer of from 0 to about 5. Arxe2x80x2 may be a single aromatic ring like hydroquinone or resorcinol, or a multiple aromatic ring like biphenol or bisphenol A.
The dihydric phenols employed are known, and the reactive groups are thought to be the phenolic hydroxyl groups. Typical of some of the dihydric phenols employed are bis-phenols such as bis(4-hydroxyphenyl)methane, 2,2-bis(4-hydroxyphenyl)propane (also known as bisphenol-A), 2,2-bis(4-hydroxy-3,5-dibromo-phenyl)propane; dihydric phenol ethers such as bis(4-hydroxyphenyl)ether, bis(3,5-dichloro-4-hydroxyphenyl)ether; p,pxe2x80x2-dihydroxydiphenyl and 3,3xe2x80x2-dichloro4,4xe2x80x2-dihydroxydiphenyl; dihydroxyaryl sulfones such as bis(4-hydroxyphenyl)sulfone, bis(3,5-dimethyl4-hydroxyphenyl)sulfone, dihydroxy benzenes such as resorcinol, hydroquinone, halo- and alkyl-substituted dihydroxybenzenes such as 1,4-dihydroxy-2,5-dichlorobenzene, 1,4-dihydroxy-3-methylbenzene; and dihydroxydiphenyl sulfides and sulfoxides such as bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfoxide and bis(3,5-dibromo4-hydroxyphenyl)sulfoxide. A variety of additional dihydric phenols are available and are disclosed in U.S. Pat. Nos. 2,999,835, 3,028,365 and 3,153,008; all of which are incorporated herein by reference. It is, of course, possible to employ two or more different dihydric phenols or a combination of a dihydric phenol with a glycol.
The carbonate precursors are typically a carbonyl halide, a diarylcarbonate, or a bishaloformate. The carbonyl halides include, for example, carbonyl bromide, carbonyl chloride, and mixtures thereof. The bishaloformates include the bishaloformates of dihydric phenols such as bischloroformates of 2,2-bis(4-hydroxyphenyl)-propane, hydroquinone, and the like, or bishaloformates of glycol, and the like. While all of the above carbonate precursors are useful, carbonyl chloride, also known as phosgene, and diphenyl carbonate are preferred.
The aromatic polycarbonates can be manufactured by any processes such as by reacting a dihydric phenol with a carbonate precursor, such as phosgene, a haloformate or carbonate ester in melt or solution. U.S. Pat. No. 4,123,436 describes reaction with phosgene and U.S. Pat. No. 3,153,008 describes a transesterification process.
Preferred polycarbonate will be made of dihydric phenols that result in resins having low birefringence for example dihydric phenols having pendant aryl or cup shaped aryl groups like:
Phenyl-di(4-hydroxyphenyl)ethane(acetophenone bisphenol):
Diphenyl-di(4-hydroxyphenyl)methane(benzophenone bisphenol):
2,2-bis(3-phenyl4-hydroxyphenyl)propane
2,2-bis-(3,5-diphenyl-4-hydroxyphenyl)propane;
bis-(2-phenyl-3-methyl4-hydroxyphenyl)propane;
2,2xe2x80x2-bis(hydroxyphenyl)fluorene;
1,1-bis(5-phenyl4-hydroxyphenyl)cyclohexane;
3,3xe2x80x2-diphenyl4,4xe2x80x2-dihydroxy diphenyl ether;
2,2-bis(4-hydroxyphenyl)-4,4-diphenyl butane;
1,1-bis(4-hydroxyphenyl)-2-phenyl ethane;
2,2-bis(3-methyl-4-hydroxyphenyl)-1-phenyl propane;
6,6xe2x80x2-dihdyroxy-3,3,3xe2x80x2,3xe2x80x2-tetramethyl-1,1xe2x80x2-spiro(bis)indane;
(hereinafter xe2x80x9cSBIxe2x80x9d), or dihydric phenols derived from Spiro biindane of formula IV: 
Units derived from SBI and its 5-methyl homologue are preferred, with SBI being most preferred.
Other dihydric phenols which are typically used in the preparation of the polycarbonates are disclosed in U.S. Pat. Nos. 2,999,835, 3,038,365, 3,334,154 and 4,131,575. Branched polycarbonates are also useful, such as those described in U.S. Pat. Nos. 3,635,895 and 4,001,184. Polycarbonate blends include blends of linear polycarbonate and branched polycarbonate.
It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with an aliphatic dicarboxylic acids like; dimer acids, dodecane dicarboxylic acid, adipic acid, azelaic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired for use in the preparation of the polycarbonate mixtures of the invention. Most preferred are aliphatic C5 to C12 diacid copolymers.
The preferred polycarbonates are preferably high molecular weight aromatic carbonate polymers have an intrinsic viscosity (as measured in methylene chloride at 25xc2x0 C.) ranging from about 0.30 to about 1.00 dl/gm. Polycarbonates may be branched or unbranched and generally will have a weight average molecular weight of from about 10,000 to about 200,000, preferably from about 20,000 to about 100,000 as measured by gel permeation chromatography. It is contemplated that the polycarbonate may have various known end groups.
In the thermoplastic compositions which contain a cycloaliphatic polyester resin and a polycarbonate resin it is preferable to use a stabilizer or quencher material. Catalyst quenchers are agents which inhibit activity of any catalysts which may be present in the resins. Catalyst quenchers are described in detail in U.S. Pat. No. 5,441,997. It is desirable to select the correct quencher to avoid color formation and loss of clarity to the polyester polycarbonate blend.
A preferred class of stabilizers including quenchers are those which provide a transparent and colorless product. Typically, such stabilizers are used at a level of 0.001-10 weight percent and preferably at a level of from 0.005-2 weight percent. The favored stabilizers include an effective amount of an acidic phosphate salt; an acid, alkyl, aryl or mixed phosphite having at least one acidic hydrogen; a Group IB or Group IIB metal phosphate salt; a phosphorus oxo acid, a metal acid pyrophosphate or a mixture thereof. The suitability of a particular compound for use as a stabilizer and the determination of how much is to be used as a stabilizer may be readily determined by preparing a mixture of the polyester resin component and the polycarbonate and determining the effect on melt viscosity, gas generation or color stability or the formation of interpolymer. The acidic phosphate salts include sodium dihydrogen phosphate, mono zinc phosphate, potassium hydrogen phosphate, calcium dihydrogen phosphate and the like. The phosphites may be of the formula V: 
where R1, R2 and R3 are independently selected from the group consisting of hydrogen, alkyl and aryl with the proviso that at least one of R1, R2 and R3 is hydrogen.
The phosphate salts of a Group IB or Group IIB metal include zinc phosphate and the like. The phosphorus oxo acids include phosphorous acid, phosphoric acid, polyphosphoric acid or hypophosphorous acid.
The polyacid pyrophosphates may be of the formula VI:
MzxHyPnO3n+1
wherein M is a metal; x is a number ranging from 1 to 12 and y is a number ranging 1 to 12, n is a number from 2 to 10, z is a number from 1 to 5 and the sum of (xz)+y is equal to n+2. The preferred M is an alkaline or alkaline earth metal.
The most preferred quenchers are oxo acids of phosphorus or acidic organo phosphorus compounds. Inorganic acidic phosphorus compounds may also be used as quenchers, however they may result in haze or loss of clarity. Most preferred quenchers are phosphoric acid, phosphorous acid or their partial esters.
Mold releases such as pentaerythritol tetra esters, especially the stearate esters. Also preferred are carboxylic acid esters of other polyols like glycerol; for example glycerol mono stearate.
In one embodiment, the polycabonate/cycloaliphatic polyester compositions may include less than about 20 percent, and preferably less than about 15 percent of an impact modifier. Typical impact modifiers generally comprise an acrylic or methacrylic grafted polymer of a conjugated diene or an acrylate elastomer, alone, or copolymerized with a vinyl aromatic compound. En general these impact modifiers contain units derived from butadiene or isoprene, alone or in combination with a vinyl aromatic compound, or butyl acrylate, alone or in combination with a vinyl aromatic compound. Other typical impact modifiers include, but are not limited to ethylene vinyl acetate, ethylene ethylacrylate copolymers, SEBS (styrene-ethylene-butylene styrene) and SBS (styrene-butadiene-strene)block copolymers, EPDM (ethylene propyleue diene monomer) and EPR (ethylene propylene rubber)copolymers, etc
According to a preferred embodiment, transparent and highly ductile compositions can be obtained via the blending of poly(cyclohexane dimethanol cyclohexane dicarboxylate) (PCCD), PC and a transparent impact modifier with a refractive index (RI) between 1.51 and 1.58. The complete miscibility of PC and PCCD allows adjustment of the RI of the PC/PCCD blend to the RI of the impact modifier. There are many impact modifiers which are suitable and some examples are given to illustrate. Examples of such impact modifiers are a clear ABS (acrylonitrile-butadiene-styrene, RI=1.535) and typical PVC modifiers like Blendex 415/336 (ABS material) supplied by GE Plastics or Paraloid ETA 702/736 (MBS material) supplied by Rohm and Haas or Kane Ace B28/B58 (S material) supplied by Kaneka. All these PVC modifiers do have a RI between 1.53 and 1.55. These parts have a unique combination of impact, transparency and chemical resistance.
Additionally, additives such as mold releases, antioxidants lubricants, nucleating agents such as talc and the like, other stabilizers including but not limited to UV stabilizers, such as benzotriazole, supplemental reinforcing fillers, and the like, flame retardants, pigments or combinations thereof may be added to the compositions of the present invention.
Adding visual effect additives like metal or mica flakes in combination with organic dyes does not result in a significant increase of the temperature where the material becomes brittle.
The multi-layer films of this invention can be transparent, or opaque as desired. Transparent products are preferred embodiments of this invention. The fluoride polymer and polycarbonate layers are first laminated together. A variety of laminating techniques can be used. However, heat lamination is preferred. Acrylic adhesives are preferred for use in the present invention.
A preferred substrate or film is one formed from a thermoplastic polycarbonate material such as previously described. Typical examples of polycarbonate resins are described in U.S. Pat. No. 4,351,920, which is incorporated herein by reference, and are obtained by the reaction of aromatic dihydroxy compounds with phosgene. A preferred aromatic dihydroxy compound is 2,2-bis(4-hydroxy phenyl)propane, (i.e., Bisphenol-A). The term aromatic polycarbonate resins is also meant to include polyester carbonates obtained from the reaction products of a dihydroxy phenol, a carbonate precursor and a dicarboxylic acid such as terephthalic acid and isophthalic acid. Optionally an amount of a glycol may also be used as a reactant. A preferred grade of polycarbonate resin for the film is LEXAN grade ML9103 available from General Electric Company. Polycarbonate film may be made by well-known methods. Typically, the molten thermoplastic is cast onto an extrusion roll stack, and both sides of the material are polished and pressed to a uniform thickness. Preferably the polycarbonate film has a thickness of from five (5) to twenty (20) mils.
It is contemplated that the film or substrate may have multiple layers which includes an outer weather resistant layer. An example of such a film or substrate are layers of a polycarbonate film layer or other transparent substrate; optionally, a layer of polyvinylidene fluoride (xe2x80x9cPVDFxe2x80x9d) film or other material resistant to ultraviolet (UV) light laminated to the polycarbonate film; and a decorated layer, which may be varied as desired, and which is printed on the exposed surface of the polycarbonate layer.
One of the most efficient and cost-effective ways of decorating a part is to do it during the molding cycle. One way to accomplish this is by inserting a decorated substrate into the cavity of a molding tool and injecting plastic behind it. This process is generally known as in-mold decoration or insert mold decoration (IMD). The decoration for the finished part can either be exposed to the environment (xe2x80x9cfirst surface decorationxe2x80x9d) and/or encapsulated between the substrate and the injected material (xe2x80x9csecond surface decorationxe2x80x9d).
Other parameters contribute to the preparation of the second surface decorated parts. First, high temperature, formable inks are preferably used for the graphics. Second surface decoration requires more robust ink systems to provide adequate ink adhesion during the molding process. Moreover, in applications such as light assemblies where light transmission is critical, dye inks should be used rather than pigmented inks so as not to affect light transmission and haze readings. Evaluation of many different inks indicates that many ink systems are not suitable for second surface decorating. Among those inks which are appropriate are the following: Naz-dar 9600, Colonial/Coates C-37 Series, Marabuwerke IMD Spezialfarbe 3060, Nor-cote (UK) IMD Series.
Prototype molds may be constructed from common materials such as plaster, hard woods, fiberglass, syntactic foam and silicone. These materials are relatively easy to work with and allow minor modifications. It is common practice for designers to experiment with IMD to cast a silicone forming mold off an existing injection mold. For example, production forming tools should be constructed of durable materials such as cast or machined aluminum, steel or metal filled epoxy. Conductive molds should be internally heated to a temperature of 250xc2x0 F.
The formed part will contract in size once it is removed from the mold and allowed to cool. The amount of shrinkage depends on the material selected, but it is predictable and must be accounted for when calculating the mold dimensions. The same is true for the expansion of the mold at operating temperatures. For example, LEXAN(copyright) polycarbonate film will typically shrink approximately 0.5-0.9% after forming, depending on the mold. The thermal expansion properties of the mold material at an operating temperature of 250xc2x0 F. must be subtracted from the film shrinkage number to obtain accurate mold dimensions. In addition, draft angles of 5 to 7 degrees are suggested to facilitate part removal from male molds. Female molds require less draft (1 to 2 degrees).
The basic considerations in gating are part design, flow, end use requirements and location of in-mold graphics. The standard guidelines of traditional gating apply to IMD along with several extra considerations. For example, one gate should be used whenever possible to minimize the potential for wrinkling the film. Gates should be located away from end-use impact as well as to provide flow from thick to thin sections to minimize weld lines. Gates should also be located at right angles to the runner to minimize jetting, splay and gate blush. Large parts requiring multiple gates should include gate positions close enough together to reduce pressure loss. Sequential gating may be used to prevent folding of the film at weld lines. Gate land lengths should be kept as short as possible. An impinging gate may be used to ensure that the incoming flow is directed against the cavity wall or core to prevent jetting. Venting (particularly full perimeter venting) may be accomplished by knock outs, cores and parting lines and should be used whenever possible to avoid trapped gas that can burn and rupture the film. In addition, flow restrictions near gate areas can increase the potential for wash out due to increased shear. If bosses, core shutoffs, etc., are needed near a gate, rounded features or corners should be used to reduce shear. Finally, care should also be taken to ensure that the gating distributes the injection pressure over a large area, thus reducing the shear forces at the gate. Examples of gates that accomplish this include fan gates and submarine gates that enter the part via a rib.
When selecting a resin, it is advantageous that the resin""s viscosity be sufficiently low such that the pressure necessary to inject it into the mold may be reduced. In addition, the injection may be profiled so that the viscosity of the injected material maintained at a sufficiently low level in the gate area and may be raised after a suitable skin layer is established near the gate. At lower viscosity, the shear force of the injected material is lower and is therefore less likely to disturb the ink on the second surface of the substrate.
It is also possible to print the graphics on the substrate so that they extend beyond the gating area and into the runner system. In this case, if the ink is disturbed by the flow of the injected material, it will be disturbed in the runner area that will be trimmed off after the part is ejected from the mold.
Of course, runnerless systems or heated gating systems may also be employed. With a runnerless system, the drop diameter must be large enough to sufficiently distribute the pressure or flow into a part, such as a rib, which does. With a heated gating system, the tips of the heated gates be maintained at a temperature sufficiently below the softening temperature of the substrate so as to prevent substrate deformation.
Screen-printing is an example of a suitable technique for producing graphics on the film substrates of the present invention. Screen-printing is essentially a stencil printing process which may now be generated by computer with the aid of various software packages. Its ability to vary and control ink thickness accurately has made it an extremely useful process for the decoration of many different types of plastic substrates.
In screenprinting, a screen or stencil is prepared and bonded to a fine weave fabric which is then tensioned in a rigid frame. Frames may be made of either wood or metal, with metal being preferred. The frame must be dimensionally stable and able to withstand handling during the printing process. Screen fabrics are generally made from metallized polyester, nylon, stainless steel, and most commonly, polyester. The fabric is tightly woven under precise control using dimensionally exact filaments. There are a number of variables that affect ink deposit, including thread diameter, squeegee angle and hardness, emulsion thickness, etc. Higher mesh screens are suggested for formed IMD applications.
The basic screenprinting process involves the use of a flat bed where the substrate is held by vacuum during printing. A frame holder positions the screen and holds it both vertically and horizontally during the printing process. With the screen lowered over the substrate bed and held at the off contact distance by the press, the squeegee carrier moves the blade across the screen at a preset speed, pressure, stroke and angle.
It is important to register artwork during a screenprinting operation. This is normally done by locking the frame into a holder that aligns the frame using pins or holders. The pin alignment method is generally preferred because the artwork can be aligned along with the screen frame. Alignment of the substrate with the print image is done through the use of edge guides, mechanical stops or automatic devices. The first color is aligned by this method and subsequent colors are aligned through the use of targets or gauge marks which are printed along side the artwork.
Once the ink is printed, it must be either dried or cured depending on the ink technology used. If the ink is solvent or water based, then a gas fired or electric dryer can be used to dry the ink. When printing on plastic films, it is important to control the temperature and dwell time in the oven to avoid distorting the film. If a solvent ink is used, it is important to use an oven with good air flow to dissipate the fumes. It is also possible to use an infrared dryer on some ink types, but particular attention must be paid to the temperature control of the system. If the ink is UV curable, many suitable commercial units are available for curing such reactive ink types.
If the final piece is three dimensional, there are two basic techniques for forming 3D IMD parts. For parts having a draw depth greater than {fraction (1/2)} inch, thermoforming is suggested. For parts containing detailed alphanumeric graphics or draw depths less than xc2xd inch, cold forming is preferred.